There's some info scattered around the different Dragons and other sources. For one thing, Derider Fanshen left her posts as Oligarch and Constable due to retirement sometime between TAB's date and the current date, to take up a post in the Temple of Pelor, IIRC.

Anyone know the story behind Tigran Gellner moving to the Militia and Sir Gavin Ambus's promotion from guildmaster of the Nightwatchmen?

Tigran Gellner has been part of Greyhawk's militia at least since 582 CY, when he appeared in the City of Greyhawk boxed set as cCommander of the Cairn Hills Force. With the death of Sental Nurev in 583, Gellner was promoted to Captain-General of the Watch, the highest military rank in the Domain of Greyhawk, which seems to automatically guarentee a chair on the Directing Oligarchy.

Ambus really didn't get "promoted," seeing as the Guild of Nightwatchmen is a private organization. The Chief Constable is second-in-command to the Captain-General; however, whereas the C-G oversees the military forces of the entire Domain, the sources imply that the Chief Constable's power and responsibilities lie chiefly within the City of Greyhawk itself. The Chief Constable seems to be another office that automatically gains a Director's chair.

Of course, since the sources state that a director who leaves office need not be replaced, granting a chair to the occupants of certain offices is likely due to the fact that it's always a wise choice to have the heads of the watch & military involved in the decision-making process.